An alternating emf is induced in a coil rotating in a magnetic field - AQA - A-Level Physics - Question 25 - 2020 - Paper 2

In a rotating coil within a magnetic field, the magnetic flux linkage is directly proportional to the angle the coil makes with the magnetic field lines. The induced emf in the coil is given by Faraday's law of electromagnetic induction, expressed as:

ext{emf} = -rac{d\Phi}{dt}

where (\Phi) is the magnetic flux. As the coil rotates, the magnetic flux linkage and the induced emf are sinusoidal but they do not reach their peak values at the same time. The relationship is such that the magnetic flux linkage reaches its maximum value a quarter cycle (or (\frac{\pi}{2} \text{ rad})) before the induced emf.

Thus, the phase difference between the magnetic flux linkage and the emf is:

• Correct answer: C) (\frac{\pi}{2} \text{ rad} )